Modelling and experimental investigation of temperature field during fly-cutting of KDP crystals

KDP crystal is the primary nonlinear crystal for making core components of inertial confinement fusion and laser frequency doublings. However, as a soft-brittle material, KDP crystal is difficult to machine due to its easy deliquescence, high brittleness, and sensitive to high temperature. A theoretical model of temperature field during fly-cutting of KDP crystals assisted by coolant lubrication was established based on cutting-heat generation theory and thermal transmission theory. This model considered the thermal exchange between the air and work material, the thermal exchange between the fluid and work material, and anisotropy of KDP crystals. The predicted results of the model indicated that oil coolant could effectively increase the thermal diffusivity and decrease the friction coefficient between cutting tools and work materials, thus decreasing the cutting temperature during the fly-cutting process. The highest cutting temperature in coolant lubrication cutting decrease by 9.42–36.70% compared with that in dry cutting. The fly-cutting experiments of KDP crystals assisted by coolant lubrication were performed to verify the model, which indicated that experimental results agreed well with predicted temperatures and the average error of the highest temperature was approximately 7.78%. Both simulated and experimental results indicated that increasing feed speed and cutting depth or decreasing the cutting speed would result in the obvious increase of the highest cutting temperature.